Method for the Production of Fire Resistant Glazing

ABSTRACT

Fire resistant glazings having improved properties comprising a silicate based interlayer which contains from 35% to 43% by weight of water may be produced using a cast in place process. The amount of water in the interlayer is reduced by concentrating the silicate solution or by introducing silica in the form of a silica sol. Preferably a mixture of an aqueous sol and an organosol is used. Polyhydroxy compounds and saccharides may be incorporated into the interlayer to improve the properties thereof and to reduce the water content. The silicate based formulations are pourable and can be used in a cast in place production process and subsequently cured to form an optically clear interlayer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.12/312,056, filed Apr. 23, 2009, which was a 371 National Phase filingof PCT/GB2007/050662, filed Oct. 30, 2007. U.S. Ser. No. 12/312,056 waspending as of the filing date of this application. U.S. Ser. No.12/312,056 and PCT/GB2007/050662 are incorporated by reference as if setforth in their entirety herein.

BACKGROUND OF THE INVENTION

This invention relates to fire resistant glazings and to methods for theproduction of fire resistant glazings.

Fire resistant glazings generally comprise laminated structures havingat least two transparent panes and at least one fire resistantinterlayer. The transparent panes are normally glass panes althoughother transparent materials such as polycarbonates may be used. Theinterlayer must be optically clear and must remain clear withoutdiscolouration throughout the lifetime of the glazing. It must alsofunction so as to improve the fire resistance of the glazing.

In many countries regulations exist specifying the fire resistanceneeded for use in particular locations. Generally these regulationsspecify either a minimum time for which the glazing must form a barrierto the propagation of a fire when one side of the glazing is exposed toa fire and/or a minimum time for which the temperature and/or theintensity of radiated heat on the side of the glazing which is notexposed to the fire must remain below a specified figure. Glass paneswill not meet any or all of these requirements and the fire resistantglazings which have been developed are laminated glazings having atleast one interlayer between at least two opposed panes.

One type of interlayer which has been developed is based upon an alkalimetal silicate waterglass. These silicate layers intumesce upon exposureto heat to form an opaque foam. The foam serves to assist the retentionof the glass panes and acts as a barrier to radiant heat.

One method for forming a silicate based interlayer is to pour awaterglass solution on to the surface of a glass pane and dry thesolution under controlled conditions to form a thin layer on the glass.A second pane may be placed on top of the dried interlayer to form afire resistant glazing. Such processes are in use in the production offire resistant glazings such as those sold by the

Pilkington Group of companies under its trade marks PYROSTOP andPYRODUR.

A second method of forming a fire resistant glazing is the so calledcast in place method in which a solution is introduced into the spacebetween two opposed panes and cured to form an interlayer. In a cast inplace process the water content of the solution is retained in the curedinterlayer. This high water content absorbs a quantity of heat during afire but the steam generated can result in fracture of the glazing. Adifficulty which is inherent in cast in place processes is the balancebetween the need for the solution to have a low enough viscosity to bepoured into the space between two opposed glass panes and the need tocure that solution to form an interlayer which is sufficiently rigid tobe retained in place throughout the lifetime of the glazing.

EP 590978 describes a cast in place process for the production of a fireresistant glass wherein the interlayer, which comprises an aqueous gelcomprising an acrylamide polymer and a particulate metal oxide, isproduced by introducing a dispersion comprising an acrylamide monomer,the particulate metal oxide and a photopolymersiation initiator betweenthe glass panes and irradiating the dispersion thereby polymerising themonomers.

EP 620781 discloses a method of producing a fire resistant glazingcomprising a silicate based interlayer using a cast in place process andglazings produced by that process. The interlayer is produced by pouringa solution which comprises an alkali metal silicate wherein the molarratio of silicon dioxide to alkali metal oxide is greater than 4:1 andat least about 44% to 60% by weight water between two glass panes. Thesolution comprises silica acid as a curing agent. After pouring thesolution is allowed to stand until it self cures to form the interlayer.

EP 981580 discloses a method for producing a fire resistant glazingcomprising a silica based interlayer using a cast in place process andglazings produced by that process in which the interlayer is obtained bypouring a solution which comprises at least 35% by weight ofnanoparticulate silica, from 10 to 60% by weight of a polyfunctionalcompound such as a polyol and from 1 to 40% by weight of a solvent.which is preferably water between two glass panes. This solution isobtained by forming a milky sol comprising the silica particles, thepolyol and water and adding an alkali metal hydroxide to the sol.

DETAILED DESCRIPTION OF THE INVENTION

We have now discovered a novel method for the production of fireresistant glazings comprising a silicate based interlayer using a castin place method which comprises combining an aqueous silicate solutionwith a silica sol to produce a mixture having a lower concentration ofwater than has previously been used. This reduced water content enablesthe production of fire resistant glazings having improved properties inparticular in so far as they exhibit a reduced tendency for theinterlayer to slump and may also exhibit improved fire resistanceproperties.

Accordingly from a first aspect this invention provides a method for theproduction of a fire resistant laminated glazing comprising a silicatebased interlayer which interlayer is formed by pouring a mixturecomprising an alkali metal silicate solution and a silica sol into acavity between two opposed glass panes and allowing the mixture to curewithout drying characterised in that the water content of the mixture isbetween 35% and 43% by weight. In the preferred processes the watercontent of the mixture is between 38% and 42% by weight.

We have discovered that the water content of the mixture may be reducedusing one of two methods or any combination of these two methods. In afirst method at least a portion of the aqueous silica sol used in theknown methods is replaced by an organic silica sol. In a second methodthe water content of the alkali metal silicate solution is reduced.Surprisingly we have discovered that these concentrated silicatesolutions, the silica sols and the mixtures comprising them are clear,that they remain pourable for a sufficient time to be useful in aproduction process and that they cure upon standing to produce a clearinterlayer having improved properties.

The organic silica sols useful in the compositions of the presentinvention comprise a dispersion of silica particles in a non aqueoussolvent. The sols will preferably comprise at least 30% by weight, morepreferably at least 40% and most preferably at least 50% by weight ofsolid material.

The solvent may be any non aqueous solvent in which the desired quantityof silica may be dispersed. It will preferably be a solvent which can beincorporated into an optically clear stable interlayer. Examples ofuseful solvents include glycerol, ethylene glycol, propylene glycol,polyethylene glycol and trimethylol propane.

The silica particles will preferably have an average particle size inthe range of from 7 nm to 50 nm. These particles are more readilydispersed in the sol and do not scatter light when incorporated in aninterlayer. The organic silica sol preferably comprises an organicallymodified silica. Such dispersions are available as articles of commerce.They are characterised by their exhibiting a lower than expected Si—OHabsorption peak in the dried form. They may be produced by forming thesilica particles in an aqueous system, removing a portion of the waterpresent and replacing it with organic material. These organicallymodified silicas have a more uniform particle size then those producedby dispersing silica particles in an organic medium. The incorporationof organically modified silica in the interlayers of the invention leadsto products having an improved fire resistance performance. The use oforganically modified silica sols represents a preferred aspect of thepresent invention.

The organic silica sols are preferably used in combination with aqueoussilica sols. These aqueous sols also preferably have a solids content ofat least 30%, preferably at least 40% and most preferably at least 50%by weight of silica. They also preferably comprise silica particleshaving a particle size of from 7 nm to 50 nm.

The relative proportions of the organic silica sol and the aqueoussilica sol will be adjusted so as to ensure that the mixture which isproduced when they are added to the silicate solution remains clear andpourable. The amount of aqueous sol which is used will also be such asto produce an interlayer comprising the desired amount of water. Ingeneral the weight of silica particles introduced in the form of anaqueous sol will be equal to or greater than that introduced in the formof a non aqueous sol. The weight introduced in the form of an aqueoussol will normally be no more than 75% by weight of the total weight ofparticulate silica.

The silica sols are combined with an alkali metal silicate solutionwherein the molar ratio of silicon dioxide to alkali metal oxide is lessthan 4:1. The amount of silica sol which is added is preferably suchthat the molar ratio of silicon dioxide to alkali metal oxide in themixture is at least 4:1 and preferably at least 4.5:1.

The silicate may be a lithium, a sodium or a potassium silicate or amixture thereof. Preferably the silicate is a potassium silicate. Alkalimetal silicate solutions are available as articles of commerce andconveniently one of these may be used. Sodium silicates wherein themolar ratio of silicon dioxide to sodium oxide is in the range 2:1 to4:1 are available as articles of commerce as are potassium silicateswherein the molar ratio of silicon dioxide to potassium oxide is in therange 1.4:1 to 2.0:1.

These commercially available solutions typically comprise from 30% up to52% by weight of solid material. They are blended with the silica solsin quantities which provide the required molar ratio of silicon dioxideto alkali metal oxide. They may be concentrated by evaporation. In thecase of potassium silicate solutions which are preferred for use in thepresent invention the solutions may be concentrated up to a level of 62%by weight of solid material.

Aqueous silicate solutions and the interlayers obtained by allowing themto cure which comprise from 35 to 43% by weight of water and from 2 to20% by weight of organic material are believed to be novel and comprisea second aspect of the present invention. Preferably the solutionscomprise from 2% to 15% and more preferably from 2% to 12% by weight ofan organic material.

The organic material may be introduced into the interlayer formulationsin the form of an organic silica sol or added separately to theformulation. Organic silica sols comprising ethylene glycol or glycerolare preferred for use in this invention. Organic materials may usefullybe added in order to modify the properties of the interlayer duringexposure to fire.

Compounds such as ethylene glycol and glycerol act as plasticizers forthe interlayer and may usefully be incorporated into interlayers whichmight otherwise be too brittle to exhibit the desired degree of fireresistance. Preferably the interlayer comprises up to 15% by weight andmore preferably from 2 to 10% by weight of glycerol or ethylene glycol.Saccharides such as sorbitol, xylitol or mannitol act to reduce thewater content of the interlayer, to bind water in the interlayer and toimprove the fire resistance of the glazing. The preferred interlayerscomprise from 0 to 10% by weight of the saccharide.

The formulation is poured into the cavity formed between two opposedpanes which are normally glass panes. The glass panes are preferablyfloat glass panes having a thickness of from 2.0 to 8.0 mm. The panesmay have a heat reflective coating upon at least one surface. Glasspanes having such a coating are well known in the art and are availableas articles of commerce.

One example of a coated glass which may be used is the low emissivityglass sold by the Pilkington Group under its trade mark K Glass.Preferably the float glass panes are toughened glass panes. The panesmay also be formed from borosilicate glasses or from ceramic glassessuch as those sold by the Nippon Electric Glass Company under the TradeMark FIRELITE.

The narrow sides of the cavity are closed using a suitable sealant whichextends around the perimeter of the panes. The width of the spacebetween the panes is preferably in the range 2 mm to 12 mm, morepreferably from 2 to 8 mm and most preferably in the range 3 mm to 6 mm.The formulation is subject to a degassing step and then poured into thecavity through an opening in the sealant. When the cavity is full theopening is closed and the glazing allowed to stand for a time which issufficient to allow the formulation to cure. The curing may beaccelerated by heating the glazing to an elevated temperature say 50 to90° C.

The invention is illustrated by the following examples. The formulationshaving the compositions presented as Table 1 were made up by premixingethylene glycol with the silica sols and the saccharide. These premixedsols were added at a steady rate to the potassium silicate solution withstirring at room temperature. The solution was degassed under reducedpressure and cast into cells made of 5 mm toughened glass with a 3 mmcavity. The solution was cured at elevated temperature to form a solidinterlayer.

Water Silica sol in content ethylene ethylene Example Molar Ratio Waterpotassium glycol glycol (50%) Sorbitol Max No Si0₂:K₂O Content %silicate % % % Size/m Fire test 1 4.7 43.9 47.6% 5 5 1.2 × 2.3 Fails EW60 2 4.7 41.0 47.6% 10 5 1.2 × 2.3 Passes EW 60 3 5.0 41.0 47.6% 10 51.5 × 2.6 Passes EW 60 4 4.7 40.0 40.4% 5 5 1.2 × 2.3 Passes EW 60 5 5.040.0 40.4% 5 5 1.5 × 2.6 Passes EW 60 6 5.0 37.0 40.4% 10 5 1.2 × 2.3Passes EW 60

1. A method for the production of a fire resistant laminated glazingcomprising a silicate based interlayer which interlayer is formed bypouring a mixture comprising an alkali metal silicate solution and asilica sol into a cavity between two opposed glass panes and allowingthe mixture to cure without drying wherein the water content of themixture is between 35% and 43% by weight.
 2. The method according toclaim 1, wherein the water content of the mixture is between 38% and 42%by weight.
 3. The method according to claim 1, wherein the silica solcomprises a mixture of an aqueous silica sol and an organic silica sol.4. The method according to claim 1, wherein the sols comprise at least30% by weight of solid material.
 5. The method according to claim 4,wherein the sols comprise at least 50% by weight of solid material. 6.The method according to claim 1, wherein the silica sol comprisesparticles having an average particle size in the range 7 to 50 nm. 7.The method according to claim 1, wherein the alkali metal silicatesolution comprises from 40% to 62% by weight of water.
 8. The methodaccording to claim 7, wherein the alkali metal silicate is a potassiumsilicate.
 9. The method according to claim 8, wherein the potassiumsilicate comprises a molar ratio SiO₂ to K₂O of at least 1.4:1.
 10. Themethod according to claim 1, wherein the molar ratio of SiO₂ to M₂O,where M represents an alkali metal cation in the mixture, is at least4:1.
 11. The method according to claim 10, wherein the molar ratio ofSiO₂ to M₂O is at least 4.5:1.